Agricultural balers are known in two types, a round agricultural baler and a square agricultural baler. The present invention is equally applicable to both the round and the square baler. The further explanation is given primarily for the square agricultural baler. However, a skilled person will readily understand how to apply the concepts explained with respect to the square baler, onto a round baler.
Agricultural balers are provided to gather crop material such as hay, straw or silage and compress the gathered crop material into a bale. To this end, a baler typically comprises a pre-compression chamber with an inlet and an outlet and a channel extending between the inlet and the outlet. The inlet of the pre-compressed chamber is connected to crop gathering means provided for gathering crop material and transferring the gathered crop material into the inlet of the pre-compression chamber. The pre-compression chamber forms slices of the gathered crop material. After a slice of crop material has been formed, it is transferred through the outlet of the pre-compression chamber into the baling chamber. A plunger reciprocally moves in the baling chamber thereby compressing the slices of crop material into a bale. The baler typically furthermore comprises knotting means for wrapping a string around the formed bale and connecting the ends of the string so that the bale is kept together after leaving the baler.
The baling chamber is defined by a plurality of baling chamber walls. A square baler comprises four baling chamber walls extending in the moving direction of the baler. A plunger is provided to reciprocally move between the four baling chamber walls at a front end of these baling chamber walls. Thereby, the plunger pushes a bale backwards in the baling chamber. The plunger exerts a force to the bale thereby both compressing the crop material into a firm package and moving the bale towards the end of the baling chamber where it can exit the baling chamber.
In order to build up pressure inside the baling chamber to compress the crop material into a bale with a pre-determined density, the baling chamber walls are formed so that the inner dimensions of the baler, at least over a part of the baling chamber length, taper towards a smaller dimension. As a result, a bale which is pushed through the baling chamber encounters an increasing frictional force. This increasing frictional force provides the backpressure that the plunger needs to obtain a bale with a pre-determined density.
Typically, square balers comprise movable wall sections, which are hinged to the baler frame in such a manner that the inner dimensions of the baling chamber can be changed by rotating the movable wall section around the hinges. Thereby, the amount of frictional force between the crop material in the baling chamber and the baling chamber walls can be regulated. Via these movable wall sections, the density of the bales can be regulated. The movable wall sections are typically moved by actuators that are connected to the movable wall section and that are powered via hydraulical or electrical systems to rotate the movable wall section around the hinge. Thereby, a controller steers the movable wall section to obtain a predetermined backpressure, which is a result of the frictional force between the crop material and the baling chamber walls.
A drawback of the known baler is that in certain situations, particularly in operating on a significantly hot day, considerably more energy is needed to obtain the required backpressure. This energy is put into the actuators for moving the wall segments towards one another in order to reduce the baling chamber diameter. By reducing the baling chamber diameter, the backpressure is increased.
With round balers, the crop material is also gathered by crop gathering means such as a pickup and transferred to the baling chamber. The round baler can have a baling chamber with a fixed diameter or with a variable diameter. In the case of a variable diameter, belts are used which constantly turn around to compress the material. When a new bale is being formed, the belts will run at a trajectory closer to the inlet of the baling chamber, while moving outwardly when the bale grows with the additional crop entering the baling chamber. The density is increased by additional tension on the belts which squeeze the bale radially. A baler having a fixed chamber will also be able to increase the density, by feeding more crop material into the baling chamber. By having more crop material for the same diameter, the density of the bale will increase.
For the round baler having a baling chamber with a variable diameter, as well as for the baler having a fixed baling chamber, the bale will be squeezed more and more radially. The bale however will try to expand axially which will increase the pressure against the walls of the bale forming chamber. The constant rotation of the bale against the walls of the forming chamber can create significant heat due to friction.